The present invention relates to a valve timing control system for an internal combustion engine which controls the opening and closing of intake and exhaust valves using a pressure sensor which senses the internal pressure in an engine cylinder.
Control apparatuses for controlling ignition timing or the quantity of fuel to be injected for an internal combustion engine in response to the internal pressure in an engine cylinder have been known. A typical example of such an ignition timing control apparatus is disclosed in Japanese Patent Publication No. 49-29209 in which peak crank positions of a piston in an engine cylinder at which the internal pressure in the engine cylinder takes a peak value are detected, and ignition timing of the cylinder is controlled in a feedback manner so as to make the peak pressure take place at prescribed piston position. Another typical example of such a fuel injection control apparatus is disclosed in Japanese Laid-Open No. 59-221433 in which the quantity of fuel to be injected into an engine cylinder is controlled based on the amount of intake air to be sucked therein which is calculated from the pressure differential between the cylinder internal pressure at bottom dead center of the piston during intake stroke and the cylinder internal pressure at a predetermined crank angle of the piston during compression stroke.
Further, it is well known that changing the opening and closed timings for the intake and exhaust valves of an engine depending upon the engine operating ranges results in improvements in the operating performance of the engine. Example of this are shown in Japanese Patent Laid-Open Nos. 64-80711 and 65-80712.
With the above-described conventional engine control apparatuses, however, valve timing control is performed in an open-loop manner, and hence accuracy in detecting the valve opening and closing timings is inadequate, so it is impossible to control the valve opening or closing timings with a high degree of preciseness.